Zinc electroplating additive

ABSTRACT

AQUEOUS ADDITION AGENTS FOR ZINC ELECTROPLATING BATHS ARE PROVIDED WHICH HAVE DISSOLVED THEREIN (A) A PYRIDINIUM COMPOUND OF THE GENERAL FORMULA:   1-R&#39;&#39;,3-R-PYRIDINIUM X(-)   WHEREIN R IS -CONH2,-CN,-CHO OR -COOR&#34;, R&#39;&#39; IS AN ALKYL GROUP OF 1-4 CARBON ATOMS, -CH2CH=CH2,-CH2C=CH, -CH2CH=CHCH2X, -CH2COOR&#34; OR   -CH2-CH=CH-CH2-(3-R-PYRID-1-YL) X(-)   R&#34; IS AN ALKYL GROUP OF 1-4 CARBON ATOM, AND X-IS A HALOGEN ION, AND (B) A POLYSTYRENESULFONATE, A POLYVINYLPYRROLIDONE, A POLYOOXYALKYLDIAMINE, A WATER-SOLUBLE QUATERIZED CONDENSATION PRODUCT OF AN EPIHALOHYDRIN AND A POLYAMINE, OR A WATER-SOLUBLE CONDENSATION PRODUCT OF A BENZENE OR A NAPHTHALENE SULFONIC ACID, OR A SALT THEREOF, WITH FORMALDEHYDE, SAID CONDENSATION PRODUCT CONTAINING AT LEAST 2 BENZENE OR NAPHTHALENE SULFONIC ACID GROUP CONNECTED WITH EACH OTHER BY METHYLENE BRIDGES.

United States Patent 3,823,076 ZINC ELECTROPLATING ADDITIVE John DerekRushmere, Wilmington, Del., assignor to E. I.

du Pont de Nemonrs and Company, Wilmington, Del. No Drawing.Continuation-impart of application Ser. No.

256,179, May 23, 1972, now Patent No. 3,769,184.

This application May 2, 1973, Ser. No. 356,432

Int. Cl. C23b 5/12, 5/46 US. Cl. 204-55 R 3 Claims ABSTRACT OF THEDISCLOSURE Aqueous addition agents for zinc electroplating baths areprovided which have dissolved therein (a) a pyridinium compound of thegeneral formula:

wherein R is CONH CN, CHO or COOR"; R is an alkyl group of 1-4 carbonatoms,

CH CH=CH CHZCECH,

CH CH=CHCH X, CH COO'R" or R is an alkyl group of 1-4 carbon atoms; andX- is a halogen ion; and

CROSS REFERENCE TO RELATED APPLICATION This is a continuation-in-part ofapplication Ser. No. 256,179, filed May 23, 1972, assigned to theassignee of the present application and now US. Pat. No. 3,769,184.

BACKGROUND OF THE INVENTION Field of Invention This invention relates tozinc electroplating baths and processes, and additives useful therein,and, more particularly, to such baths and processes for depositingbright zinc plates.

Prior Art Numerous patents concerned with bright zinc deposits obtainedfrom acid zinc baths have issued over the years. US. Pat. 3,537,959,issued Nov. 3, 1970, to Joachim Korpiun and Hans J. Steeg, is directedto the co-use of primary amines and naphthalene sulfonicacid-formaldehyde condensation products for this purpose. The co-use ofquaternized pyridines with linear polyethers for acid zinc plating isdisclosed in German Pat. 2,111,602, published Mar. 18, 1970. Mycopending application Ser. No. 157,662, filed June 28, 1971, disclosesthe use of certain quaternized pyridine compounds in acid zinc plating.Other patents directed to the use of sulfur and nitrogen compoundsinclude US. Pat. 2,355,505, issued to John L.- Bray and Robert E. Howardon Aug. 8, 1944, and US.

3,823,076 Patented July 9, 1974 "ice Pat. 2,543,545, issued to CharlesL. Faust and Arthur E. Bearse on Feb. 27, 1951, which discloses the useof sulfonated heterocyclics.

Quaternary pyridine compound additives useful in alkaline cyanide zincplating are described in US. Pat. 3,318,- 787, issued to Gustav Rindtand Donald H. Becking on May 9, 1967, and certain pyridinium compoundsuseful in alkaline zinc plating are described in US. Pat. 3,411,996,issued to John D. Rushmere on Nov. 19, 1968.

SUMMARY OF THE INVENTION According to the present invention there isprovided an addition agent for an aqueous zinc electroplating bathcomprising an aqueous solution containing (a) about 1-25 percent byweight of a pyridinium compound of the general formula:

wherein R is CONH CN, CHO or COOR; R is an alkyl group of 1-4 carbonatoms,

R" is an alkyl group of 1-4 carbon atoms; and X- is a halogen ion; and

DETAILED DESCRIPTION OF THE INVENTION This invention pertains to theelectrodeposition of zinc from zinc plating baths known to those skilledin the art. These baths may be formed by the dissolution of zinc oxidein common industrial acids such as hydrochloric, sulfuric, sulfamic andfluoboric. More commonly, however, the baths are formed by thedissolution of commercial zinc and ammonium salts such as the sulfates,chlorides, acetates, fluoborates or sulfamates in Water with subsequentadjustment of pH to the normal or desired range by means of aqueousammonia, ammonium hydrox' ide or other bases, or an acid as required.

While the bath pH will generally be at a slightly acidic pH between 3.5-and 6.5, a higher pH bath, such as to pH 7.5, may be used, by theaddition of a base such as ammonium hydroxide. However, for thisinvention, it is preferred to operate at a pH between 5 and 6.5 whenusing the preferred zinc chloride baths.

In zinc chloride baths, ammonium chloride is added to improve electricalconductivity and to help complex zinc ions, thereby increasing boththrowing power and high temperature operability. Zinc metal content ofthe bath will range from about 545 g./l., preferably 5-20 g./1., mostpreferably 6-9 g./l. The Cl/Zn weight ratio will range between about 4/1and 30/1 depending on the zinc metal content of the bath, the ratiobeing limited by bath temperature and ammonium chloride solubility.Thus, very good performance using the additives of this invention can beobtained from a bath containing 15 g./l. Zn, Cl/Zn ratio of 10/1, pH5.1, and temperature of operation 10-45 C., preferably 20-30 C. Afurther improvement in performance can be obtained by using a bathcontaining 7.5 g./l. Zn, Cl/Zn ratio of 25-30/ 1, pH 6.1, andtemperature of operation 10-50 0, preferably 20-45 C.

Bath formulations may contain mixtures of zinc salts such as zincchloride and zinc sulfate. However, there appears to be little practicaladvantage for doing this. Bath formulations may also contain other metalsalts such as a conductivity increasing salt, like sodium sulfamate orpotassium sulfate.

Zinc deposits obtained from such acid baths without additives aretypically coarse and dull gray in appearance and have little commercialvalue, especially in decorative plating of screws, chains and otheritems of hardware. It has now been found that when an additivecombination comprising a mixture of certain quaternized pyridinecompounds with a polystyrenesulfonate, a polyvinylpyrrolidone, apolyoxyalkyldiamine, a water soluble quaternized condensation product ofan epihalohydrin and a polyamine, or water-soluble condensation productsof an aryl sulfonic acid with formaldehyde is added to the acid zincbath, bright, shiny zinc of high decorative quality can be obtained fromboth barrel plating and rack plating operations. The pyridiniumcompounds useful in the present invention have the [general formula:

p wherein R is -CONH CN, CHO or COOR"; R' is an alkyl group of 1-4carbon atoms,

R" is an alkyl group of 1-4 carbon atoms; and

X is a halogen ion, preferably chlorine, bromine or iodine.

The pyridim'um compound is used at a concentration level of about 0.02to 20 grams per liter, preferably about 0.05

to 5 grams per liter.

Preferred pyridinium compounds are l-allyl, 3-carboxamido pyridiniumhalide where the halide is chloride, bromide or iodide. Other compoundsthat have been found useful include:

The second component of the additive is a polystyrenesulfonate, apolyvinylpyrrolidone, a polyoxyalkyldiamine,

a water-soluble quaternized condensation product of an epihalohydrin anda polyamine, or a water-soluble condensation product of a benzene ornaphthalene sulfonic acid, or salt thereof (usually alkali metal), withformaldehyde containing at least two benzene or naphthalene sulfonicacid groups which are connected with each other by means of methylenebridges. A naphthalene sulfonic acid is preferred. Preparation of theseproducts is known and one such method is mentioned in US. Pat.3,537,959. The second component is added in an amount to give a bathconcentration of about 0.5 to 50 grams per liter, preferably about 1 to20 grams per liter. The particular concentration used and foundeffective will depend upon the type and amount of pyridinium compoundused and whether rack or barrel plating is being used.

The brightener combination of the present invention is preferably andeffectively used as an aqueous solution addition agent containing about1 to 25 percent by weight, preferably about 1 to 10 percent, of thepyridinium compound and about 1 to 50 percent by weight, preferablyabout 1 to 20 percent, of the condensation product. A particularlyeffective addition agent uses l-allyl, 3-carboxamido pyridinium chlorideas the pyridinium compound and the sodium salt of a naphthalene sulfonicacid-formaldehyde condensation product. The addition agent is normallyused by adding about 5 to 20 ml. of solution per liter of bath althoughlarger amounts (such as up to 50 ml./l. can be used with effectiveness).

The invention can be further understood by referring to the examples inwhich parts and percentages are by weight unless otherwise indicated.

In conducting the following examples, a basic zinc chloride bathcontaining:

ZNCl

g /l 32 NH Cl g /1 200 pH 5.1

was used unless otherwise noted. Temperature of operation was 2228 C.again unless otherwise noted.

EXAMPLE 1 A steel Hull Cell panel was plated at 2 amps for 5 minutes inthe basic bath containing 2.0 g./l. Darvan #1 and 2.0 g./1. l-propargyl,S-car-boxamido pyridinium bromide.

Very bright plate free of pits was obtained over the current densityrange 2-60 amps/ft.

EXAMPLE 3 To a 4-liter basic zinc chloride bath were added 65 cc. of anaqueous brightener containing 15 percent of a watersoluble condensationproduct between alkyl naphthalene sulfonic acid and formaldehyde (Daxad1 1) and 6 percent 1-al1yl, 3-carboxamido pyridinium bromide. Anautomobile steel crank hold cover, a shape comprising both concave andconvex surfaces, was still plated with no agitation at 2 amps for 20minutes. (Current density approximately 20 amps/ftfi.) Shiny bright zincwas deposited on all surfaces including the recesses. The deposit tookan excellent chromate conversion coating. Daxad products are made andsold by W. R. Grace Co. of Cambridge, Mass.

EXAMPLE 4 30 g. #6 x /2" steel wood screws were barrel plated in aminibarrel at 2 amps for 20 minutes in the basic bath containing 2.0g./l. Darvan #1 and 0.4 g./l. 1- allyl, 3-carboxamido pyridiniumbromide. A very bright lustrous zinc deposit was obtained. The deposittook both a nitric acid bright dip and a chromate conversion dip withoutdifficulty.

EXAMPLE 5 A 30 g. load of #6 x /2" steel wood screws was barrel platedat 2 amps for 20 minutes in the basic bath containing 1.0 g./l. of awater-soluble condensation product between benzene sulfonic acid andformaldehyde (Darvan #2) and 0.4 g./l. l-allyl, 3-carboxamido pyridiniumbromide. A shiny bright product was obtained.

Another 30 g. #6 x V2" steel wood screws were likewise barrel plated inthe basic bath containing only 1.0 g./l. Darvan #2. The screws were dullmatte gray and of unacceptable commercial quality.

A third 30 g. load of screws was likewise barrel plated in the basicbath containing only 0.4 g./l. l-allyl, 3-carboxam'ido pyridiniumbromide. Again the screws were dull gray and of unacceptable commercialquality.

EXAMPLES 6-11 Minibarrel plating tests were conducted on 30 g. loads ofscrews, plated at 2 amps for 20 minutes, using the basic zinc chloridebath to which had been added 2.0 g./l. Daxad #11. In addition,quaternized pyridines were added in the amounts stated and with theresults shown in Table I.

was added as brightener 2.0 g./l. Darvan #1 and 0.8 g./l. l-allyl,3-car-boxamido pyridinium bromide. 30 g. of screws were barrel plated at2 amps for 20 minutes in a minibarrel using this bath. As plated theywere semibright. After dipping in 0.5 weight percent nitric acid,brightness was improved and they were of acceptable commercial quality.

EXAMPLE 14 A 4-liter basic zinc chloride bath containing 32 g./l. ZnCland 200 g./l. NH Cl was operated at pH 5.1 for 610 ampere hours ofbarrel plating electrolysis using a 10 percent by weight aqueousbrightener containing 2.5 parts of a. water-soluble condensation productbetween naphthalene sulfonic acid and formaldehyde and 1 part ofl-allyl, 3-carboxamido pyridinium chloride. Average temperature ofoperation was 20-25" C. and the bath was producing fully bright zincdeposits. Temperature of the bath was raised successively to 30 C., 35C., C. and C. As the temperature was raised, brightness was lost fromthe deposit, more particularly the liquid luster. However, work ofacceptable commercial quality was obtained, after bright dipping, evenat 45 C.

EXAMPLES 15-21 In examples 15 to 21 tabulated below, are recorded theresults of 267 ml. Hull Cell tests on various polymerl-allyl,3-carboxamido pyridinium bromide (ACPB) combinations. The tests wereconducted at 2025 C. using the basic chloride bath containing 15 g./l.Zn, Cl/Zn=10/1 and pH 5.1. Electrolysis current was 1.5 amps for 5minutes.

Amount ACPB Deposit Example Amount polymer (g./i.) (a./it. Appearance 154 g./l. Verse-TL" 70 0. 8 0:2 E 16 2g.ll. Verse TL" 400.. 0.8 6 A brightP 0. 4 0-80 Bright with some dull streaks. g ll "Ionac PE-100 0. 8Brilliant above 6 a./i't.

. "Ionac" PE-llO- 0.8 Brilliant above 15 e../it.

.ll. Ionac PE-120 0.8 Brilliant above 12 a./it.=

./l. J efiamine" ED-600 0. 8 Brilliant above 6 a./1t.

TABLE I Ex. Amount No. Additive (g./l.) Results 6 1-propargyl, 3-carbo-0. 04 Acceptable commercial rnethoxy pyridinium product after nitricbromide. acid bright dip.

7 l-allyl, 3-cyano 0. 08 Semibright, very nice pyridinium bromide; shinybright roduct after bright p.

8"-.. l-allyl, 3-iormyl 0. 2 Semibiight. Bright shiny pyridiniumbromide. giroduet after bright 9"..- 2-butene 1,4 bis (3- 0. 08 Verybright and shiny carboxamido after bright dip. pyridinium bromide).Brittle deposit.

10.--- 1-(4-ch1orobutene-2) 0. 4 Bright shiny deposit Bearboxamido afterbright dip. Dark pyridinium bromide. color.

11.... l-carbomethoxy methyl 2 Shiny bright product S-earboxamido afterbright dip. pyridinium bromide.

EXAMPLE 12 EXAMPLE 13 To a zinc sulfate bath containing: ZnSO -7H O Q/l.. 250 (NH SO g /l.. 30 pH 3.8

Versa-TL 70 and Versa-TL 400 are polystyrenesulfonates (sodium salts),average molecular weights 70,- 000 and 400,000 respectively, supplied byNational Starch and Chemical Company of Plainfield, NJ.

PVP is polyvinylpyrrolidone, grade K15, average molecular weight 10,000,supplied by GAF Corporation of 140 W. 51st St., New York, N.Y.

Ionac PE-lOO, PEI-110, PE-120 are quaternized condensation products ofepihalohydrins and polyamines manufactured and supplied by IonacChemical Division of Sybron Corporation of Birmingham, N.J., accordingto the teachings of US. 3,642,663.

Jeflamine ED-600 is a polyoxyalkylidamine, average molecular weight 600,supplied by I elferson Chemical Corporation of Houston, Tex.

EXAMPLE 22 A -liter bath containing 7.5 g./l. Zn, Cl/Zn weight ratio of25 1, and pH 6.1 was operated continuously using a 10 wt. percentbrightener solution containing 2.5 parts of a water-soluble naphthalenesulfonic acid-formaldehyde condensation product and 1 part of l-allyl,S-carboxamido pyridinium bromide. After an initial 2 1. addition ofbrightener, miscellaneous work pieces (bolts, nuts, washers, screws,hinges, etc.) were barrel plated so as to deposit about a 0.2 milthickness of zinc at temperatures of 25C., 35 C., 43 C., and 51 C. Nobrightness loss was observed in raising temperature from 25 C. to 35 C.Some brightness loss was observed at 43 C. but was restored by adjustingthe Cl/Zn ratio to 30/1. Some further loss in brightness was experiencedat 51 C. which could not be restored either by brightener or ammoniumchloride additions.

What is claimed is:

1. An aqueous addition agent for a zinc electroplating bath comprisingan aqueous solution containing (a) about 1 to 25 percent by weight of apyridinium compound of the general formula:

wherein R is CONH CN, CHO or -COOR"; R is an alkyl group of 14 carbonatoms,

--CH CH=CH -CH CHECH,

R" is an alkyl group of 1-4 carbon atoms; and X- is a halogen ion; and

or naphthalene sulfonic acid groups connected with each other bymethylene bridges.

2. The addition agent of Claim 1 wherein the concentration of thepyridinium compound is about 1 to 10 percent by weight and theconcentration of said other compound is about 1 to 20 percent by weight.

3. The addition agent of Claim 2 wherein the pyridinium compound isselected from the group consisting of l-allyl, 3-carboxamido pyridiniumhalide; l-methyl, 3- carboxamido pyridinium halide; l-propargyl,3-carboxamido pyridinium halide; 1-(4-chlorobutene-2), 3-carboxamidopyridinium halide; 2-butene 1,4 bis (3-carboxamido pyridinium halide);l-carbomethoxymethyl, 3-carboxamido pyridinium halide; l-propargyl,3-carbomethoxy pyridinium halide; 1-allyl, 3-cyano pyridinium halide andl-allyl, 3-formyl pyridinium halide, wherein the halogen is chlorine,bromine or iodine; and wherein said other compound is a water-solublecondensation product of a naphthalene sulfonic acid, or a salt thereof,with formaldehyde, said condensation product containing at least 2naphthalene sulfonic acid groups connected with each other by methylenebridges.

References Cited UNITED STATES PATENTS 3,318,787 5/1967 Rindt et al 204-Y 3,411,996 11/1968 Rushmere 204-55 Y X 3,734,839 5/ 1973 Hoyer et al.204-55 Y 3,755,097 8/1973 Cope 204-55 Y GERALD L. KAPLAN, PrimaryExaminer US. Cl. X.R.

204Dig. 2

